MPEG Dynamic Adaptive Streaming over HTTP (DASH)
MPEG doc#: N11964
Date: March 2011
Author: Iraj Sodagar
Dynamic Adaptive Streaming over HTTP specification provides a standard for delivering multimedia over Internet.
The following figure shows the conceptual architecture for DASH.
This specification defines two formats in the above architecture:
1) The Media Presentation Description (MPD) which provides sufficient information for a DASH client for adaptive streaming of the content by downloading the media segments from a HTTP server.
2) The segment formats which specify the formats of the entity body of the request response when issuing a HTTP GET request or a partial HTTP GET.
DASH provides a standard solution for the efficient and easy streaming of multimedia using existing available HTTP infrastructure (particularly servers and CDNs, but also proxies, caches, etc.). It enables the deployment of the streaming services using the existing low cost and wide-spread Internet infrastructure without any special provisions. It supports both on-demand and live streaming. While DASH is format and codec agnostic, and can be used with any media format, it has specific provisions for the MPEG-4 file format and MPEG-2 Transport Streams. Since the streaming session is controlled by the DASH client, the HTTP server does not need to cope with the additional load of stream adaptation management in large scale deployments. DASH also allows the client the choice of streaming from various CDNs, and therefore achieving further load-balancing of the network for the benefit of the client. DASH provides dynamic switching between different media tracks (e.g. varying by bit-rate, to adapt to network conditions), with the possibility of seamless switching. It also enables dynamic ad-insertion and slicing of various live and on-demand content. It allows signaling, delivery and utilization of multiple content protection schemes. In DASH, the MPD can be fragmented and delivered in parts to reduce the session start-up delay. The MPD can be also updated during the streaming session. DASH’s MPD supports expression of content accessibility features, rating, and camera views. DASH also supports delivering of multi-view and scalable coded content.